-LRB- CNN -RRB- -- When 48-year-old Erin Peiffer , of Eldersburg , Maryland , learned that she had high cholesterol in her 20s , she never thought it would pose a problem .

When she was 39 , Erin Peiffer , now 48 , had open-heart surgery to unblock her left main artery .

Although her overall cholesterol number lingered in the low to mid-200s , she figured her medication would keep it under control .

But she figured wrong , and heart disease slowly started clogging her arteries .

Dr. Elizabeth Nabel , director of the National Heart , Lung and Blood Institute at the National Institutes of Health in Bethesda , Maryland , says that over the years , it 's become clear to most American women that heart disease is nothing to ignore . It 's the leading cause of death of women in the United States , says Nabel , a prominent advocate for women 's heart health .

But Nabel says many women still do n't know all the risk factors for heart disease , especially when it comes to cholesterol .

`` For middle-aged women , 40 to 60 , high cholesterol is the single most important risk factor for heart disease and heart attacks , '' she said . The Heart Truth : How to lower your risk for heart disease

Peiffer did n't think much about her cholesterol until nine years ago , when , at age 39 , she began to feel ill during a water aerobics class .

`` I started coughing , '' she recalled . `` I was coughing a lot ! ''

It got so bad she decided to drive home . The cough , she says , grew worse . `` The coughing continued , but then I was coughing up this pink , frothy stuff , and I knew that was n't right . ''

Alarmed , Peiffer left her kids with her husband and drove herself to the hospital . But because of her age , doctors never considered that she might be having heart problems ; they figured she had a virus and sent her home . But later tests showed that she had something wrong with her heart . After performing an angiogram , her doctors told her the bad news . Watch more on women and high cholesterol ''

`` They told me I had a 99 percent blockage in my left main artery , '' she said . `` I needed open-heart surgery . ''

Millions of Americans get a diagnosis of high cholesterol every year . Cholesterol comes from two sources : your body and your food . Your liver -LRB- and to a smaller degree , your cells -RRB- makes about 75 percent of blood cholesterol . The remaining 25 percent comes from the foods you eat .

Cholesterol is divided into two main types . HDL , or high-density lipoprotein , is the `` good '' cholesterol because it helps to clear excess fats from the arteries . LDL , or low-density lipoprotein , is the bad cholesterol because it clogs the arteries , increasing a person 's risk for heart attack and stroke .

The American Heart Association says that in premenopausal women , estrogen tends to raise HDL -LRB- good -RRB- cholesterol . But as estrogen drops during menopause , HDL levels drop too , and LDL levels rise . That 's why women need to know their numbers .

For years , physicians believed that hormone-replacement therapy was a good way to protect a woman 's heart . However , the heart association recommends that hormone replacement not be used for cardiovascular protection , because recent studies have shown that postmenopausal women using it received no real heart benefit .

In some people , improving diet and adding exercise can lower the overall number , but when lifestyle changes do n't work and for people who have a genetic predisposition for high cholesterol , medication is usually prescribed .

But cardiologists say many people think that because they are taking medication , they 're protected and do n't need to worry about their numbers . That 's just not the case .

So what are good cholesterol levels ? Your overall cholesterol number should be under 200 . If you have other risk factors -- like smoking , high blood pressure or a family history of heart disease -- your doctor may want it lower .

A good HDL level of 60 mg or greater is considered protective . LDL should be under 100 mg for those with no risk factors for heart disease and 70 mg for those at higher risk . But again , depending on your health and family history , your doctor may want different readings .

The first step in fighting high cholesterol is simple : `` Get a blood test , '' Nabel said .

The National Cholesterol Education Program guidelines recommend that everyone age 20 and older get a fasting `` lipoprotein profile '' every five years . It gives your doctor information about total cholesterol , LDL , HDL and triglycerides , which are the main type of fat in blood .

If your numbers are unhealthy , your doctor can advise you on treatment . If you want to avoid medication and try to achieve healthy cholesterol numbers naturally , the American Heart Association has these recommendations :

• Keep your weight down , and cut down on calories , especially from saturated and trans fats , carbohydrates and alcohol . Even small amounts of alcohol can lead to large changes in triglyceride levels -LRB- although red wine may slightly bump up good cholesterol -RRB- .

• Eat plenty of fruits , vegetables and nonfat or low-fat dairy products . And add fish to your diet . Fish oil helps reduce cholesterol .

• Get off the couch and get active . Even 30 minutes of moderate exercise , five days a week or more , can make a difference .

After her surgery , Peiffer had her family members ' cholesterol levels checked . She found that two of her three children had high numbers , and they are now on medication .

Today , Peiffer too takes her medication , eats right and exercises to keep her heart healthy . And most important , she knows her numbers : Her cholesterol is well below 200 .

She said , `` I tell anyone , anyone who will listen -- my family , friends -- ` Know your cholesterol numbers . ' It could save your life . ''

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Heart disease is leading cause of death of women in the United States

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Expert : For middle-aged women , high cholesterol is the most important risk factor

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Millions of Americans get a diagnosis of high cholesterol every year

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Cholesterol comes from two sources : your body and your food